Tin is used to bloom or brighten colors, especially reds, oranges and yellows. Its general effect is to give brighter, clearer and faster color than the other mordants. However, it is not so useful as a mineral mordant in itself, but as a modifying agent with other mordants. It is almost always used with cream of tartar — ½ ounce tin and 1-2 ounces of cream of tartar for a pound of wool. When used as a mordant before dyeing, the wool is entered into the cold mordant bath, containing 4 per cent of stannous chloride and 2 per cent oxalic acid; the temperature is gradually raised to boiling, and kept at this temperature for 1 hour. It is sometimes added to the natural dye bath towards the end of dyeing, to intensify and brighten the color. It is also used with cochineal for scarlet on wool in the one bath method.
Tin must always be used with great care, as it tends to harden the wool, making it harsh and brittle. Too much tin makes wool brittle. It is caustic, be sure to handle carefully and clean up thoroughly. While mordants such as chrome, copper and tin all metallic salts work well to fix the dyes and provide an alternate palette, they can be a health hazard and produce toxic waste which will require special disposal. Mordants such as alum, iron, and tannin are safer to use and can produce myriad colors when used in conjunction with the appropriate natural dye.